Problem: What is $80\%$ of $50$ ?
Answer: Having $80\%$ of something means that you get $80$ out of every $100$ We can set up a proportion to find out what number is $80\%$ of $50$ $ \dfrac{{\text{percent}}}{100} = \dfrac{{\text{part}}}{{\text{whole}}}$ Which things do we know, and what are we trying to find? We know the ${\text{percent}}$ is $80$ . Is $50$ the ${\text{part}}$ or the ${\text{whole}}$ The $50$ is the ${\text{whole}}$ . We are trying to find the ${\text{part}}$ that makes up $80\%$ of it: $ \dfrac{{80}}{100} = \dfrac{{\text{part}}}{{50}}$ If we divide the denominator of the fraction on the left by $2$ , it will be the same denominator of the fraction on the right. To keep things equal, let's also divide the numerator on the left by $2$ $ \dfrac{{80} \div 2}{100 \div 2} = \dfrac{{\text{part}}}{{50}}$ $ \dfrac{{40}}{50} = \dfrac{{\text{part}}}{{50}}$ $ {40} = {\text{part}}$ So $40$ is $80\%$ of $50$.